This invention relates to an electric field intensity measuring device suitably employed in the open air under severe weather conditions and more particularly, to a rotary electric field intensity measuring device of the above type which includes a pair of electrode means having alternating voltage inducing means, respectively.
An increasing number of open air leisure facilities such as golf courses for example, have been and being built even in regions where thunderbolts quite frequently stike and as a result, increasing attention has been paid to safety of players playing and employees working in such leisure facilities and regulations relating to personal safety in the open air leisure fecilities have become more and more severe.
When it is forecasted that a thunderbolt seem to stike in a golf course, it is necessary to evacuate the players and employees rapidly out of the golf course to a safe location. In order to determine whether the players and emplyees should be evacuated out of the golf course or not, a number of thunder alarms have been developed and practically operated and as one most advanced or improved type thunder alarm, devices adapted to detect the electric field intensity on the surface of a selected ground and provide an alarming signal in response to the detection of a particular value of electric field intensity have been developed. Of the most advanced thunder alarming devices, the so-called rotary electric field intensity measuring devices have been most often accepted because of their simplicity in construction and high reliability in performance.
When the rotary electric field intensity measuring device is operated in the open air rather than in a laboratory for the under forecast, in practice, it is particularly important to ensure that the device perform its function properly without being adversely affected even when exposed to wind and rain and provide a reliable and precise measuring result.
However, the conventional rotary electric field intensity measuring device has the disadvantages that the insulation between the opposed charge induction faces and ground deteriorates when the device is operated in heavy rain and that the space defined between the charge induction faces is soon filled with rain water to thereby electrically connect the charge induction faces together throughout their area resulting in substantial reduction in induced voltage. In order to eliminate the disadvantages inherent in the conventional rotary electric field intensity measuring device, an insulator having a high resistance (silicone, for example) is usually employed between the charge induction faces and ground. Although the use of such a high resistance insulator may improve the insulation, electrostatic charge remains on the surface of the insulator for a long time after the deactuation of the device and will not disappear easily which may tend to cause error in measuring of electric field intensity by the device. Due to the disadvantages inherent in the conventional rotary electric field intensity measuring device referred to hereinabove, the timing of thunderbolt discharge will not always correspond to the electric field intensity measured by the measuring device. Thus, when the conventional rotary electric field intensity measuring device is operated as a thunder alarm for forecasting thunderbolt discharge, the device encounters difficulties in forecasting the timing of thunderbolt discharge with preciseness.